An electrophoresis procedure which has been developed for the separation of large DNA molecules will be applied to yeast chromosomal DNA. Chromosome-specific probes available as recombinant-DNA molecules will be used to moniter separation by electrophoresis, and develop additional procedures. Specific yeast chromosomal DNA fragments containing cross-links will be isolated and examined to elucidate the nature of the cross-links. The associated DNA will be mapped with restriction endonucleases, and the sequences adjacent to different cross-links will be compared. The observation that 2 micron plasmid replication is restricted to the S-phase of the cell cycle will be re-examined using a selection synchrony technique. Pre- and post-replication molecules will be examined for possible initiation-related modifications. A more quantitative test of meiotic transmission will be performed.